Claude Opus 5.5 Fast Mode exits preview, enabled via speed field

Anthropic has made Fast Mode generally available for Claude Opus 5.5 with no waitlist and no beta header: speed is turned on with a "speed": "fast" field in the Messages API request. Pricing is $8 per million input tokens and $40 per million output tokens, available on the Claude API and Microsoft Foundry on Azure, but not in the Batch API or on Bedrock.

• Fast Mode is enabled with "speed": "fast"; the beta header is no longer required
• Pricing: $8 per 1M input and $40 per 1M output tokens across the full context
• The thinking parameter now returns a 400 error; use effort (low/medium/high) instead
• Not available in the Batch API, AWS Bedrock, or for Opus 5 and 4.8